Laminated magnetic material

ABSTRACT

An extrusion billet is fabricated from layers of soft magnetic material separated by one or more metal layers. The billet is coreduced and heat treated to impart the desired magnetic properties to the soft magnetic material and also to form intermetallic insulating layers between the magnetic layers. Electric field shield sections are formed in a similar manner by placing relatively thick layers of copper between adjacent layers of metal located adjacent to the layers of soft magnetic material. The layers of soft magnetic metal can also be separated by a layer of semiconductor material; or a metal foil having a semiconductor-forming or high electrical resistivity forming material deposited thereon. In the latter case no extrusion is required. Instead, pressure and heat cause the materials to react and form either a semiconductor layer or a layer with an electrical resistivity higher than about 10 4 ohm-cm between adjacent layers of soft magnetic metal. Even the deposition step is eliminated by separating and bonding the layers of soft magnetic metal with glass so long as the glass and soft magnetic metal have similar coefficients of thermal expansion.

United States Patent [1 1 Whetsone 51 Apr. 29, 1975 1 LAMINATED MAGNETICMATERIAL [76] Inventor: Clayton N. Whetsone, l 100 Penn Central Blvd,Pittsburgh, Pa. 15235 [22] Filed: May 3, 1973 [21] App]. No.: 356,893

Related US. Application Data [63] Continuation-impart of Ser. No.79.864, Oct. 12.

1970, Pat. No. 3.756.788.

Primary E.\'uminer-L. Dewayne Rutledge Assistant E.\'aminerE. L. WeiseAttorney, Agent. or FirmGriffin, Branigan and Butler [5 7] ABSTRACT Anextrusion billet is fabricated from layers of soft magnetic materialseparated by one or more metal layers. The billet is coreduced and heattreated to impart the desired magnetic properties to the soft magneticmaterial and also to form intermetallic insulating layers between themagnetic layers. Electric field shield sections are formed in a similarmanner by placing relatively thick layers of copper between adjacentlayers of metal located adjacent to the layers of soft magneticmaterial. The layers of soft magnetic metal can also be separated by alayer of semiconductor material; or a metal foil having asemiconductor-forming or high electrical resistivity forming materialdeposited thereon. 1n the latter case no extrusion is required. lnstead.pressure and heat cause the materials to react and form either asemiconductor layer or a layer with an electrical resistivity higherthan about 10" ohm-cm between adjacent layers of soft magnetic metal.Even the deposition step is eliminated by separating and bonding thelayers of soft magnetic metal with glass so long as the glass and softmagnetic metal have similar coefficients of thermal expansion.

30 Claims, 9 Drawing Figures MENTEUAPMQIQH SHEET 1 BF 3 FIG. I

FIG. 2

FIGS

FIG. 6

LAMINATED MAGNETIC MATERIAL BACKGROUND OF THE INVENTION This is acontinuation-in-part of my copending application Ser. No. 79,864 filedon Oct. 12, 1970 now U.S. Pat. 3,756,788, dated Sept. 4, 1973. Thisinvention relates to laminated magnetic materials and more particularlyto a method for making such materials so that the resulting structurehas qualities that are particularly suited for use in connection withalternating current applications such as transformer cores, magneticrecording heads, and shields for electric and magnetic fields.

High permeability soft magnetic materials are frequently used fortransformer cores, and magnetic heads or the like. In such cases, thehigh permeability soft magnetic laminates are held together withelectrically insulating organic compounds in order to reduce eddycurrent losses; and it is an object of this invention to provide both animproved structure of this type and a method for making the improvedlaminate.

In accordance with present methods of manufacturing high permeabilitylaminates, individual layers of soft magnetic material are first heattreated at around lOOOC in order to impart the desired qualities of highpermeability. The thusly heat treated soft magnetic layers are thenbonded together with the organic insulating compounds by a hand process.The heat treating, however, leaves the magnetic layers physically softso that they have a tendency to bend during the bonding step; and thisbending causes both non-uniformity and deterioration of the magneticqualities of both the individual soft magnetic layers and, the resultingstructure.

In addition, in order for the laminated product to have acceptablemoderate and high-frequency performance characteristics, the layers ofmagnetic material are preferably quite thin. That is, on the order ofabout 0.001 inch. Consequently, the soft magnetic layers are usuallyderived from thinly rolled stock which has an inherent set or curvatureresulting from the rolling operation. When the magnetic layers arelaminated, therefore, they are flattened out and in so doing additionalstresses are created which result in a further deterioration of theuniformity and quality of the structures magnetic properties. Moreover,the bonding process itself causes certain additional stresses; andfrequently laminated cores are spongy as a result of a bubble or bondingdefect in the organic binder. It is therefore another object of thisinvention, to provide a laminated magnetic material that is of uniformpermeability and coercivity; and substantially free of the abovedescribed stresses and defects so as to result in a product havingvastly superior and uniform magnetic qualities.

During the above described hand bonding step the soft magnetic layersare frequently so severely bent that the resulting laminate is entirelyunsatisfactory for its intended purpose. If such bending is detectedduring fabrication, the individual laminae can be discarded. This issomewhat costly; but not as serious as when the bent layer is onlydetected after fabrication in which event it is necessary to discard theentire finished assembly containing the laminated structure. Moreover,only a relatively small amount of bending is required before a laminateddevice must be discarded. This, therefore, results in a very highscrap-loss rate in the industry. Consequently, it is another object ofthis invention to provide a method of fabricating uniform laminatedmagnetic materials which eliminates both the hand bonding steps and thehigh scrap-loss rates.

Because of the above-described difficulities in handling the thin layersof magnetic material, it is not practical to use layers that are thinnerthan about 0.001 inch. This however, puts a severe limitation on thefrequency ranges with which such structures can perform satisfactorily.Hence, it is another object of this invention to provide a laminatedmagnetic material having far thinner soft magnetic layers and a methodof manufacturing such structures wherein the problems of handling suchthin layers are eliminated. An attendant object, of course, is toprovide a laminated structure such as a recording head having superiorhigh frequency performance characteristics.

Another object is to provide a laminated magnetic material that can beused as a shield for electrical and magnetic fields.

It is frequently desired that two or more recording heads be matched. Inthis regard, a pair of heads might well have high quality performance,but still be unsatisfactory for a given application because of certaindifferences in their performance characteristics. Because of theuniformity of the structures fabricated in accordance with theprinciples of this invention it is relatively simple to provide elementsthat are both matched and admirably suited for high peformanceapplications.

Another advantage of the invention results from the insulating layershaving a much greater hardness than the magnetic layers so that thelaminate has vastly improved wear characteristics particularly when usedin magnetic head applications. In fact, in some instances where it isnot necessary to improve a given structures high frequency responsecharacteristics, it is more important to obtain increased wearqualities, particularly where the manufacture of such a structureresults in lower costs, more uniformity, and lower scraploss rates.Hence, it is another object of this invention to provide magneticlaminates which both maintain the high frequency responsecharacteristics of currently available devices and provide better wearcharacteristics.

It is still another object of this invention to provide a laminate whichincorporates any of the above described objectives and advantageswithout requiring either a coreduction step, a vapor deposition step, oran electroplating step.

. SUMMARY OF THE INVENTION In accordance with the principles of thisinvention a laminate is formed wherein layers of soft magnetic metal areseparated by a layer of insulating material whose electrical resisitivtyis substantially higher than that of the soft magnetic metal and whereinthe laminate can be heated to the annealing point of the soft magneticmetal after the laminate is formed, thus imparting to the soft magneticmetal the optimum permeability in the finished product.

In one embodiment of the invention an extrusion billet is fabricatedfrom layers of soft magnetic material each separated by one or morelayers of an insulative compounding material. That is a material whichcan be reacted with its adjacent layer to form one or more intermetallicelectrically insulating compounds. The billet materials are thencoreduced to a desired thickness and heat treated to form intermetallicinsulating layers and impart the desired magnetic properties to the softmagnetic material.

In accordance with other principles of this aspect of the invention thearticles into which the laminated structure is to be fabricated areshaped, such as by a blanking operation, prior to the heat treatingstep. In this manner, the heat treating step removes the stressesdeveloped during the shaping of the laminate into the configuration ofits ultimate product.

In accordance with a still further principle of this aspect of theinvention the time and temperature of the heat treatment are selected sothat a small amount of the material between the soft magnetic layers ispermitted to diffuse into the soft magnetic material itself. In someapplications this has been found to increase the resulting structuresfrequency characteristics.

Also, where it is desired to form a section to shield or concentrateelectric fields one or more layers of highly conductive shieldingmaterial such as copper are placed between adjacent magnetic layers.This is particularly useful, for example, in a multi-track tape headembodiment where adjacent head sections are separated from each other bythe electric field shielding section. In this manner the magnetic layersshield magnetic fields and the conductive layers shield electric fieldsto result in an easily fabricated composite structure which shields bothmagnetic and electric fields and prevents cross talk between adjacenthead sections. Alternatively, laminated shielding sections can be madeseparately and used in a host of applications for shields are such, andquite aside from their use in combination with recording heads or othertransformertype embodiments.

It will be appreciated from the foregoing summary of this aspect of theinvention that it provides a simple method of forming a high qualitylaminated without the previously required hand operations which are bothcostly and decidedly detrimental to the uniformity and overallperformance of the resulting product. Moreover, in transformer-typeapplications the ultimate products frequency-response characteristicsare easily controlled by among other things varying the thickness ratiobetween the magnetic material and the insulating material; and theamount of coreduction to which the billet is subject.

In some instances it is desirable to avoid the coreduction stepdescribed above. Hence, in accordance with other principles of theinvention, the layers of soft magnetic metal are separated by one ormore layers of elements which, when heated form a highly resistive layerhaving a resistivity of more than about ohm-cm. For example, a group Velement such as arsenic or antimony is plated onto a foil of a group IIImetal such as aluminum and placed between layers of soft magnetic metal.The resulting laminate is then subjected to heat and pressure to fullyreact the materials to form highly resistive layers such as a hardsemiconductor layer between the layers of soft magnetic metal. Byeliminating the former organic binders, this embodiment still permitsthe soft magnetic metal to be annealed to recover its high permeability,even though the permeability is not further increased by an additionalreduction in thickness. This embodiment, therefore, results in astructure having a uniformly high permeability and good wearcharacteristics without obtaining the greatly improved high frequencyresponse resulting from the very thin soft magnetic metal layers thatare obtained using the coreduction embodiment.

A variation of the embodiment just described is obtained by merelydepositing a semiconductor such as selenium, or a simple insulator suchas silicon monoxide, onto the layers of soft magnetic metal prior totheir being stacked into a laminate. The structure is then merely heatedunder pressure to obtain bonding of the laminate which displays bothhigh permeability and good wear characteristics.

Both of the immediately preceding embodiments include the step ofplating or otherwise depositing onto either the soft magnetic metal or aseparate metal foil, elements that combine to form a continuous layerwith a resistivity greater than about 10 ohm-cm. In accordance withother principles of the invention, even those steps can be eliminatedwhere layers of glass are substituted for the layers of insulativecompounding material separating the layers of soft magnetic metal. It ismerely necessary that the glass layers have a coefficient of thermalexpansion that is similar to that of the soft magnetic material toprevent thermal stresses from lowering the permeability on cooling fromthe annealing temperature of the glass. When this method is used, notonly can coreduction be eliminated, but no costly vapor-deposition orelectro-deposition steps are required; and, if increased wear is themain desired feature of the structure, it is not even necessary to heatthe resulting laminate to the annealing temperature of the soft magneticmetal, because adequate bonding can be obtained between the glass andthe soft magnetic metal by merely heating the laminate above thesoftening point of the glass.

Gaseous elements can also be included within the laminate. For example,if it is desired to further improve the hardness of the insulatinglayer, the entire method can be carried out in one of the mannersdescribed above and then gas is diffused into the high resistance layerby heating the laminate in a gas rich atmosphere. In fact, the resultingstructure can even be ground and polished before the gas diffusion step.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects,features, and advantages of this invention will be apparent from themore particular description of preferred embodiments thereof asillustrated in the accompanying drawings wherein the same referencenumerals refer to the same elements throughout the various views. Thedrawings are not necessarily intended to be to scale, but rather arepresented so as to illustrate the principles of the invention in a clearform.

In the drawings:

FIG. 1 is a schematic of the cross section of a laminated billet priorto coreduction.

FIG. 2 is an enlarged fragmentary view of FIG. 1 taken along lines 2-2thereof;

FIG. 3 is a schematic of an alternate embodiment of the structureillustrated in FIG. 2;

FIG. 4 is a photomicrograph of structure similar to that of FIG. 2 afterit has been coreduced;

FIG. 5 is a photomicrograph of the FIG. 4 structure after it has beenheat treated;

FIG. 6 is a schematic cross-sectional view of a shield-' ing laminatefabricated in accordance with principles. of the invention;

FIG. 7 is a schematic cross sectional view of a composite structurecomprised of both a FIG. 2 or 3-type laminate and a FIG. 6-typelaminate;

FIG. 8 is an exploded schematic view illustrating the fabrication of oneof the embodiments of the invention;

and

FIG. 9 is a fragmentary sectional view taken along lines 9-9 in FIG. 8.

DETAILED DESCRIPTION A first aspect of the invention is illustrated inFIG. 2 wherein layers of soft magnetic material 10 are separated bylayers 12 ofa suitable insulating compounding material which, whenheated reacts with the soft magnetic material to form an electricallyinsulative compound of elements that are covalently bonded instoichiometric proportions otherwise referred to as an electricallyinsulative intermetallic compound. A desired number of these variouslayers 10 and 12 are made into a sandwich 14 and placed in an etchresistant casing 16 as illustrated in FIG. 1.

The casing 16 and its enclosed sandwich 14 are then placed in anextrusion can 18 and a filler material 20 having mechanical propertiessimilar to that of the magnetic material is placed between the sides ofthe can 18 and the casing 16. End caps (not shown) are then welded ontothe can to close its ends; and, in this regard, one of the caps includesan evacuation tube so that the can can be evacuated after the end capsare welded in place. Once the can is thusly evacuated the tube ispinched-off" and welded closed to retain a vacuum inside can 18.

The resulting structure 22 of FIG. 1 is then suitably heated andextruded through a laminar-flow die so that the layers 10 and 12 arecoreduced and diffusion bonded.

After extrusion the can 18 and filler sections 20 are removed from thebillet such as by etching while the etch resistant casing 16 protectsthe coreduced sandwich 14.

FIG. 4 is a photomicrograph of the laminated portion of an actuallyextruded billet to be described in more detail shortly. Briefly,however, FIG. 4 is a IOX magnification of an extruded laminate comprisedof layers of soft magnetic material 24 that have been coreduced withintervening layers 26 of a material with which the magnetic layers 24will form intermetallic compounds during a heat treating step to bedescribed shortly. It should be noted, however, that the layers 24 and26 are diffusion bonded as indicated by the dark lines 28.

Preferably, the FIG. 4 laminate is next shaped into its ultimate productform. For example, toroids having square cross sections are machined orblanked out of the extruded flat stock. The shaped pieces are thendeburred and etched to remove metal which might be smeared across theedges of the laminations.

The extruded stock or shaped elements, as the case may be, are next heattreated in a generally conventional manner to anneal the magneticmaterial and impart to it the desired high permeability and low coerciveforce qualities. Heat treatment of magnetic material to improve itsqualities is already discussed in the literature. Hence, it will not bediscussed in detail herein. It should be carefully noted, however, thatduring the heat treating step in this invention the diffusion coupleillustrated by the lines 28 in FIG. 4 give rise to the formation ofintermetallic compounds such as those within bracket 30 in FIG. 5. Inthis regard, the magnetic material 24 in FIG. 4 is annealed to form thelarge grained bands 32 in FIG. 5; and the layers 26 in FIG. 4 arelocated in the center 34 of the bracketed layers 30 in FIG. 5. Theremaining layers such as 36, 38 and 40 in FIG. 5 are first, second andthird intermetallic compounds of the soft magnetic material and theinsulating compounding material.

It is an important aspect of this portion of the invention that thelayers between the magnetic materials form insulative intermetalliccompounds wherein elements unite in definite atomic proportions similarto true chemical compounds, but do not follow simple valence rules. Inthis connection it is preferred that the laminations 12 in FIG. 2 becomprised of a refractory metal such as niobium, tantalum, zirconium,titanium, hafnium, or vanadium. The selection of such laminae in anygiven instance, however, depends upon the type of magnetic materialused; and whether the sandwich 14 includes additional layers as will bedescribed shortly in connection with the FIG. 3 embodiment. That is,depending upon the other materials in the sandwich, the layers 10 and 12are selected to provide at least one layer of an insulativeintermetallic compound during the heat treating step.

The above described refractory metals are preferred because of theirhigh melting point and good formability but primarily because they formmany insulative intermetallic compounds both between themselves and withiron and nickel in the adjacent layers of soft magnetic material. Othermetals such as magnesium, aluminum, zinc, and cadmium are also suitablebecause they too form insulative intermetallic compounds, albeit fewerin number. Certain rare earths are also suitable. In this regard, phasediagrams showing intermetallic compounds within binary systems are shownin Constiration of Binary Alloys by Max Hansen, 2nd Edition, publishedby McGraw-l-Iill Book Co., N.Y., 1958; and, Constitution of BinaryAlloys, First supplement; by Rodney P. Elliot, McGraw-Hill Book Co.,N.Y., 1965. Of course intermetallic compounds are also formed in ter'nary and quaternary alloys. But such formations are complex and will notbe discussed further except to note that binary phase diagrams providestrong guidelines as to what can be expected from the more complexalloys; and refer to a discussion of intermetallic compounds and theirproperties in Intermetallic Compounds, J. H. Westbrook, Wiley & Sons,NY.

The FIG. 3 embodiment is otherwise similar to that described aboveexcept that additional layers 44 are placed between the layers ofrefractory metal 12 and the layers of magnetic material 10. In thisregard, the material for the layers 44 is selected so as to form anintermetallic compound with the material of layer 12, but not harm theconventional magnetic qualities of the material 10. Again, althoughspecific metals will be noted shortly, the above noted properties ofmany suitable metals and alloys are available in the literature and willnot be discussed in detail herein.

In one specific embodiment of the invention the soft magnetic material10 was comprised of Hy Mu 800", a trademarked product of the CarpenterSteel Corporation containing 79% nickel, 16% iron, and 4% molybdenum.This alloy is a single phase, or solid solution alloy, with the crystalstructure of nickel; and, when properly heat treated, exhibits highpermeabilities and low coercive forces. Each layer 10 was 0.007 inchthick, about 2 inches wide, and about 5 inches long.

The particular embodiments layers 12 were of commercial grade zirconiumabout 0.0007 inch thick. In this regard, the relative thicknesses of thelayers and 12 are selected to obtain a high quantity of magneticmaterial while still having enough of the compounding metal to obtaingood electrical insulating characteristics over the desired frequencyrange of operation for the ultimate product. Thickness ratios of 10 to 1thru to l are preferred. The ratio can go to 50 to l, but fabricationbecomes more costly because of the extensive coreduction required.Ratios of as little as 3 to I also provide better gain than currentlyavailable products, but the gain at these relatively low ratios isconsiderably less than the gain of structures having thickness ratioswithin the preferred range. Moreover, when low thickness ratios areused, the annealed product tends to include a relatively thick layer ofinsulating compounding material corresponding to layer 34 in FIG. 5.Where space is a consideration, however, it is preferable that all ormost of the insulating compound material be reacted to form insulatingintermetallic compounds; in which event there is little or no layercorresponding to layer 34 in FIG. 5.

The above described Hy Mu 800/zirconium sandwich 14 was surrounded by alayer of titanium which served as the etch resistant barrier 16. Thesandwich and barrier were then placed in a low carbon steel can 18 and alow carbon steel filler metal 20 was employed because of the similaritybetween its metalurgical characteristics and those of the Hy Mu 800.Another example of a suitable filler metal would be a copper-nickelalloy because it too has metalurigcal characteristics similar to thoseof Hy Mu 800. Of course, other types of filler metals might be usedwhere other types of magnetic metals are employed; and in this respectit should be noted that any soft magnetic material may be used. Otherexamples of suitable soft magnetic materials can be found inFerromagnetism by Richard M. Bozorth, published by Van Nostrand, NewYork, 1951; and Metals Handbook by Metals Handbook Committee of ASM,published by ASM, l96l, pages 785-797.

After the assembly 22 was evacuated it was heated to 700C and extrudedthrough a A: inch laminar flow die where the layers were coreduced anddiffusion bonded. The extruded billet was then sprayed with a ferricchloride etching solution to remove the low carbon steel can and fillersections. In this regard, the titanium was selected because it is notattached by the ferric chloride so that both the titanium and thesandwich were left intact. Hence, the result of the etching step was arectangular array having the cross section of that depicted in the FIG.4 photomicrograph. The sandwich was then further reduced by rolling to0.020 inch.

Toroids having a square cross section were then machined out of theextruded flat stock; and the toroids were deburred and etched in ahydroflouric acid-nitric acid solution to remove metal that had smearedacross the edges of the lamination.

Next some of the toroids were heat treated at 900C for two hours andpermitted to cool while they remained in the heating furnace. Thisresulted in the magnetic layers 32 being in their fully annealed stateas indicated by the large grain size and the terminal twins (widebandsin the grains) in FIG. 5. Although not fully illustrated in the I350XFIG. 5 photomicrograph the interdiffusion between the layers ofzirconium and Hy Mu 800 resulted in the formation of substantially allof the possible intermetallic compounds that might be predicted from theNiZr phase diagram. The layer 40 in FIG. 5 however, is probably thefirst electrically insulative intermetallic compound of zirconium and HyMu 800 and, therefore, highly resistive compared to Hy Mu 800.

As noted, some of the toroids that were machined from the extruded flatstock were withheld from heat treatment. Both these and the annealedtoroids were then wound into a transformer configuration and comparedwith a similar structure made in accordance with conventionaltechniques. In this regard, a known alternating current was applied atgiven frequencies to the primary of each transformer; and the voltageoutputs from the secondaries of the transformers were measured by a highimpedance voltmeter (l0 megohms). Particularly at high frequencies to bediscussed shortly, the EMF across the secondary of the transformerhaving the annealed toroids of the invention was much higher for thesame drive current than the EMF developed across the unannealed toroids.In addition, the transformers having the annealed toroids of theinvention exhibited sharp resonant frequencies resulting from theincreased capacitive effect of the intermetallic insulative layers whichwere thus proven to have been obtained during the heat treatment.

More significantly, the transformers comprised of the inventionsannealed structure were several orders of magnitude better than theconventionally structured transformers. That is, the structure of theinvention had a better response at a frequency of 10 megahertz than theconventional transformer type core exhibited at 60 kilohertz. Moreover,the structure of the invention had an excellent constancy of responsewhile the conventionally structured transformers was down by a factor offive when its input frequency reached 10 kilohertz.

In two other more particular embodiments of the invention the sandwich14 was structured in accordance with FIG. 3. In one, 0.007 inch thicklayers 10 of Hy Mu 800 were separated by a composite layer comprised ofa 0.0007 inch thick layer of titanium (12 in FIG. 3) between adjacentlayers 44 of oxygen free high conductivity copper (OFHC) having aboutthe same thickness as the titanium. Copper was selected because it wasnot known to have any harmful effects upon the magnetic properties ofthe Hy Mu 800 when diffused into it; and it was also known that copperwould form a intermetallic insulative compound with titanium. In theother embodiment cadmium was substituted for the titanium layer 12. Theremainder of the method of fabrication was the same as that describedabove; and the test results were equally satisfactory. Hence, it is notnecessary that the intermetallic compound be formed with the magneticmaterial itself. Moreover, it has been found that the resultingstructures frequency response improves when there is diffusion of anintermediate metal such as copper into the magnetic metal. After apoint, of course, extensive such diffusion would indeed harm themagnetic qualities of the magnetic material itself, but up to that pointit has been found helpful to encourage such diffusion. In the Hy Mu800/coppertitanium embodiment, for example, it was found that up to 6%of the copper could be satisfactorily diffused into the Hy Mu 800.

Preferably the intermediate layer of copper 44 in FIG. 3 should not bemuch, if any, thicker than the layer of insulative compounding material.In fact, for transformer-type applications it is preferred that theintermediate layer of highly conductive metal be suffciently thin thatit is substantially completely reacted during the annealing step to formintermetallic compounds in place of the original intermediate layer.This is not to say that the resulting transformer-type embodimentscannot retain an unreacted layer of the intermediate metal, but eddycurrent losses increase as the thickness of such a layer increases; andthe advantages of the intermediate layer are dissipated as its thicknessapproaches that of the soft magnetic material. Still other embodimentswere substantially the same as those just described except that thecopper was replaced by nickel and the results were about the same.

Another embodiment of the invention is schematically illustrated inconnection with the shield structure of FIG. 6. Therein a shieldsandwich 148 is comprised of layers of copper 46 that were realtivelythick was compared with intermediate layers 44 in the FIG. 3 embodiment.These layers 46 were placed between adja cent layers 48 of titanium andsoft magnetic material 10. In this regard, both the copper and magneticmaterial layers were 0.007 inches thick and the titanium was 0.0007inches thick. The embodiment was otherwise fabricated in the same mannerdescriibed above. In this case, however, the titanium layers 48 formedinsulative intermetallic compounds with both the soft magnetic material10 and the thick copper layers 46. These intermetallic compounds weresimilar to layers 36, 38, and 40 in FIG. 5; and the resulting copperlayers were sufficiently thick to act as an electric field shield.Hence, after the billet was coreduced and blanked the copper layers 46served as electric field shields and the magnetic layers (correspondingto layers 32 in FIG. 5) served as magnetic field shields.

Inasmuch as the highly conductive layer 46 is used as an electricalfield shield it must not be so thin that it is all reacted during theannealing step. In fact it should be at least three times as thick asthe layers 48 of insulative compounding material; and it is preferredthat the layers 46 be sufficiently thick that there be about the samethickness remaining after the intermetallic compound reaction as thereis remaining in the layers of soft magnetic material. But insofar asshield performance is concerned, and commensurate with-spacelimitations, the highly conductive layer can be much thicker if desired.In some shielding applications it is not necessary to insulate theconductive layers 46 from the soft magnetic layers 10. Hence, in thosecases layer 48 may be omitted.

One application of the above described shielding embodiment is tosimultaneously form such a structure in combination with thetransformer-type structure of FIGS. 2 and 3. That is, as illustrated inFIG. 7 the extru sion billet is comprised of a first sandwich of layers14 such as those illustrated in FIG. 2 and a second sandwich 145 ofshielding layers such as those illustrated in FIG. 6. After coreductionand shaping the transformertype sections resulting from sandwiches 14are connected into a driven or receiving magnetic circuit M, but theshielding sections resulting from sandwich 148 are not. In this manner,the shielding sections shield the transformer-type sections from eachother so that the composite structure of FIG. 7 is admirably suited foruse in multi-track recording heads wherein each of the transformer-typesections serves its own track and its adjacent shield section preventsit from receiving cross talk from the other transformer-type sections.In the above regard, it should be appreciated by those skilled in theart that the circuit M is intended to be broadly illustrative. Forexample, the dotted lines do not indicate that the sections 14 areconnected together and the circuit m can certainly include electriccircuit portions.

It will be apparent that the above described method is far moresatisfactory than conventional techniques; and, because hand bonding isnot required the scraploss rate is relatively negligible. Of course, theincrease in frequency response in structures made in accor dance withthis aspect of the invention is dramatic. Moreover, because of theuniformity between the various elements fabricated from a given piece ofextruded flat stock, all of the elements fabricated from the piece arematched," Hence, the expense and difficulty of obtaining matchedelements has been eliminated. Also, because the intermetallic compoundsare quite hard and resulting laminate is highly resistant to wear whichis a significant advantage particularly in magnetic recording headapplications.

While this aspect of the invention has been particularly shown anddescribed with reference to preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention. For example, layers of additional materials can beused between the layers of soft magnetic material; and although aninitial diffusion bonding step has been described in connection with anextrusion die, similar bonding can be obtained by rolling or pressing.In addition, the insulative compounding materials can include gaseouselements; and they can be electroplated, vapor deposited, or otherwiseplaced on the soft magnetic material instead of being placed in thesandwich by hand. Also, other techniques can be used to separate thecoreduced layers from the extrusion can; and additional layers can beadded to the billet sandwich. Similarly, although dimensions of thesandwich elements have been specified above they are not as significantas their ratios. The final thicknesses of the various layers are moreimportant to frequency response and these can be controlled by theamount of coreduction to give magnetic layers as thin as 0.0001 inches.

As noted above, coreduction can be eliminated by using some other highlyresistive material instead of materials that react to form intermetalliccompounds. In this respect, in one embodiment arsenic was deposited to athickness of about 0.0005 inch on an aluminum foil 0.0007 inch thick. Alaminate similar to that of FIG. 2 was then formed of a soft magneticmetal (Hy Mu 800) and the arsenic coated foil. Next, the stack wassubjected to pressure and heated to the annealing temperature of thesoft magnetic metal. As this occurred the arsenic and aluminum reactedto form a semi-conductor or an essentially electrically insulating layerbetween each layer of soft magnetic metal. The resulting laminate wasthen ground and polished before testing.

In another aluminum foil embodiment, a 0.00063 inch layer of antimonywas deposited on 0.0007 inch aluminum foil which was then laminated withsoft magnetic metal. This laminate was then heated to the annealingtemperature of the soft magnetic metal. As this occurred, diffusionbonding took place between the antimony and the soft magnetic metal; andthe aluminum reacted with the antimony to form a semiconductor or anessentially electrically insulating layer. The diffusion bonded portionwas probably not insulative in nature, but the resulting semiconductorlayer was sufficiently electrically insulative that the resultinglaminate had excellent overall properties for use in magnetic heads, forexample.

Inasmuch as the layers of soft magnetic metal (about 0.001 inch thick)were not further reduced in thickness, the resulting structures highfrequency response was not increased as dramatically as in the coreducedembodiment described above. There was some increase in the highfrequency response characteristics with respect to conventionallaminates of similar thickness, however, because the soft magnetic metalwas annealed after lamination to remove the fabrication stresses whichwould not have been removed during construction of a conventionallaminate. In addition, the scrap-loss rate in the conventional laminateis much larger; the laminates according to this aspect of the inventionare much more uniform; and the laminate of the invention has vastlygreatly resistance towear because of the hardness of the highlyresistive layers.

In other embodiments of this aspect of the invention the highlyresistive materials as such as deposited directly onto the soft magneticmetal layers so that there is no need to react two layers to form ahighly resistive layer. Selenium, for example, is vapor deposited on asoft magnetic metal and stacked to form a laminate in the mannerdescribed above in order to obtain a laminate having characteristicssimilar to those described for the arsenic-aluminum embodiment. Siliconmonoxide is also used to obtain similar results. In fact, if highfrequency response characteristics are not of sufficient importance tothe particular product in which the laminate is placed, it is not evennecessary to heat the composite laminate to the annealing temperature ofthe soft magnetic metal. It is only necessary to heat the structure toprovide adequate bonding to obtain the desired high wear resistance thatis afforded by the hardness of the semiconductor or other highlyresistive layer.

Additional semiconductors or other highly resistive combinations ofelements can also be used. For exam ple, the layer between the softmagnetic metal in FIG. 2 can be comprised of selenium deposited on lead,tin, or hafnium. Other examples are cadmium sulfide, lead sulfide,cadmium oxide, zinc sulfide, zinc oxide, nickel oxide, germaniumsulfide, tin sulfide; and other compounds having similar energy gapssuch as those set forth in the Handbook of Chemistry and Physicspublished by the Chemical Rubber Company, Cleveland, Ohio. In the1972-1973 Edition (53rd) such semiconductor elements are listed at pagesE-89 through E-92.

The semiconductor embodiments require some type of deposition suchas-plating, vapor'depositing, or the like. The aspect of the inventionabout to be described, however, even eliminates such deposition steps.In this regard, it has previously been suggested that layers of similarmaterials be sintered or otherwise bonded together to form magneticlaminates. U.S. Pat. No. 3,478,340 to Schwartz describes such a method.In those cases, however, extremely highly resistive ceramic typepowdered ferrites are bonded with powdered ceramics per se to form highcoercivity laminates having wide hysteresis loops. That is, Schwartzuses ferrites having resistivities in the range of 10 to l0" ohmcm ascompared with 10 or so ohm-cm for the soft magnetic metals of theinstant invention.

One of the objects of the instant invention, has been to bond dissimilarmaterials such as low-resistivity, soft magnetic metal having lowcoercivity and narrow hysteresis loops with relatively electricallyinsulative material in a manner so that the soft magnetic metal layerscan be annealed after fabrication without destroying the bondtherebetween. Previously soft magnetic metal layers were bonded byorganic binders such as epoxy which, even at moderately elevatedtemperatures, breakdown causing the laminate to come apart.

Provided certain requirements are met, it has been found that the aboveobjectives can even be obtained by laminating glass with soft magneticmetal and heating them to form a bond therebetween. Basically, it ismerely necessary to ensure that, after annealing, the soft magneticmetal maintains its high permeability and the layers remain adequatelybonded. Hence, the glass and the soft magnetic metal are selected sothat their coefficiently of thermal expansion are similar throughout thetemperature range from the strain point of the glass to the temperatureat which the resulting structure is to be used.

In the above regard, glass has virtually no crystal structure, but itnevertheless has several significant temperature points that are definedby using the viscosity of the glass as a reference. Fluid glass is saidto be above its working temperature. Somewhat below this in temperatureis the softening point and below that the annealing point. The strainpoint" or setpoint of the glass is at a still lower temperature. Belowthe strain point, glass can no longer compensate for strain so thatstresses can be introduced into the glass. Such stresses can be removed,however, by heating the glass to its annealing temperature. No stressescan be introduced above the strain point. Hence, the temperature rangeover which the coefficients of expansion between the soft magneticmaterial and the glass must be compatible, extends from the strain pointof a given glass to room temperature (or the temperature at which theresulting structure is to be operated).

In one embodiment of this aspect of the invention the soft magneticmetal was Hy Mu 800; and the glass was that identified in theKirk-Othmer Encyclopedia of Chemical Technology (2nd Edition, 1965) asCorning 1990. This particular glass had a softening point of 500 C; anannealing point of 370 C; a strain point of 340 C: and was comprised of41% silicon dioxide, 40% lead oxide, 12% potassium oxide, 5% sodiumoxide,

' and 2% lithium oxide.

With reference to FIG. 8, layers of frets are alternated with layers ofglass 62. In this regard, the frets are conventional sheets of softmagnetic material having elements 64 photoetched therein. Theillustrated elements 64 are tape head sections; and the glass iscomprised of sheets of powdered glass formed into a tapelike structureby a volatilizable organic binder such as that described in U.S. Pat.No. 3,371,001.

The soft magnetic frets are about 0.001 inches thick.

After they are cleaned they are located by holes 66 over=locating pins68 extending upwardly from a platen 70. The alternate layers of glassare about 0.0002 inch thick to. form a laminate such as that shown inFIG. 9

wherein the layers 60 correspond to layers in FIG. 2 and the layers 62correspond to layers 12 inFlG. 2. The platen assembly is then placed inafurnace and heated in an oxygen containing atmosphere. The organicbinder volatilizes without leaving an undesirable residue. The glass isthen heated sufficiently that it bonds the layers of soft magneticmetal. That is, the glass is heated to at least its softening pointwhich, in this case, is 500C.

A weight 72 is then located by means of holes 74 on pins 68 above boththe bonded laminate 61 and thickness-cont ol blocks 76. The entirestructure is then placed in an evacuated retort or other oxygen-freeencapsulation to prevent oxidation during a subsequent heating step toanneal the soft magnetic metal (about (600C to 1200C in the case of HyMu 800). In this manner, the weight 72 compresses the laminate to itsdesired thickness as determined by the height of the gauge blocks 76 andthe soft magnetic metal is fully annealed so that its fabricationstresses are removed.

The annealed laminate is then subjected to a conventional cooling cyclefor the particular soft magnetic metal that is employed. For Hy Mu 800,for example, a cooling rate of about 195C 280C per hour is employed fromthe metals annealing temperature, through its Curie temperature (about460C for Hy Mu 800), to a temperature somewhat below the Curietemperature (370C in this case). In order to prevent stresses that canoccur from thermal gradients, the laminate was cooled from 370C to 40Cat 100C/hr and then removed from the furnace.

Finally, the fully annealed laminate is cut into desired shapes, ground,and polished in a conventional manner. The permeabilities of laminatesconstructed in the manner just described were excellent; and comparedwith commercial organically bonded laminates having soft magnetic metallayers of the same thickness (0.001 in.) are as follows:

Hence, it is apparent that the method of the invention results in agenerally improved permeability; and, in addition, results in astructure having vastly superior wear characteristics; a lower straploss rate; and more uniformity. Perhaps most significantly, however,because commercial laminates having organic binders cannot be annealedafter fabrication, they cannot be satisfactorily laminated with ultrathin foils of soft magnetic metal. 0.001 inch foils are presently apractical minimum. With the instant invention, on the other hand,beginning foils can be an order of magnitude thinner because theresulting fabrication stresses can be removed during the annealing stepafter basic fabrication. When these ultra thin foils are employed withthe method of the'invention, the resulting laminates high frequencyresponse characteristics increase by a factor that is roughly inverselyproportional to the thickness.

Since presently commercially available organic laminates do not havesuch thin soft magnetic metal layers, comparative data cannot beeprovided. It should be abundantly clear, however, that the method of theinvention provides not only moderately increased permeability andgreatly increased wear for laminates having standard thicknesses of softmagnetic material, but the high frequency permeability increasesdramatically as the thickness of the soft magnetic material is decreasedin the manner permitted by the method of the instant invention.

Other glasses can be combined with other soft magnetic metals to achieveresults similar to those described above so long as the metal and theglass have generally similar coefficients of thermal expension. In theabove example, for instance, the coefficients of expansion for both the1990 glass and the Hy Mu 800 were virtually the same at both roomtemperature and the strain point (sometimes called set point) of theglass. In this respect, the mean thermal expension coefficient from 25Cthru 300 C for the 1990 glass was about 137 X 10 inches per inch per C;while that of the Hy Mu 800 was about 136 X 10' inches per inch perdegree C. The change in length per unit length of the glass between 25Cand its strain point (340C) was 433 X 10*, while for the Hy Mu 800 overthis temperature range it was 430 X l0 and the maximum differencebetween the two was about X 10 inches per inch occurring at about 200C.In this regard, it presently appeaars that although expansiondifferences greater than 500 parts per million can be tolerated undersome conditions; differences of parts per million cause relativelylittle trouble. Hence, for purposes of this invention thermal expensioncoefficients can be considered as being substantially the same even ifthey differ by over 500 parts per million.

Many, many other combinations of glasses and soft magnetic metals areequally satisfactory. For example, My Mu 800 can be used with Corning0110 or 9776.

The composition of 0110 is 50% SiO 19 /2% K 0; 6% Na O; 10% BaO; 5 /2%A1 0 7.2% C210; and 1.8% F. The composition of 9776 is 88% PbO and 12% B0 When using some of the very low softening point glasses, however, itmay not be desirable to subsequently heat the laminate to the annealingpoint of the soft magnetic layers in order to prevent the glass frompossible deterioration. Similarly, Corning glass 6810 can be laminatedwith a soft magnetic metal containing 42% nickel and 58% iron. The glassin the example has a composition of: 56% silicon dioxide; 10% aluminumoxide; 1% boron trioxide; 7% sodium oxide; 1% potassium oxide; 4%calcium oxide; and 3% lead oxide; and has a mean thermal coefficient ofexpansion of 69 X 10 inches per inch per degree C from 0 C through 300C. The mean thermal coefficient of expansion for the soft magneticmetal, is also about 69 X 10 inches per inch per degree C from 25 Cthrough 450 C.

Another suitable laminate is comprised of Corning glass 8871 and a softmagnetic metal alloy comprised of 50.5% nickel and 49.5% iron. The glasscomposition is 42% silicon dioxide; 1% lithium oxide; 2% sodium oxide;6% potassium oxide; and 49% lead oxide. The mean coefficient of thermalexpansion of the glass from 0 C through 300 C is 102 X 10' inches perinch A further listing of thermal coefficients of expansion appears inthe above noted Bozorth publication at page 643 et seq. Further listingsappear in Cartech Alloys for Electronic, Magnetic, and ElectricalApplications, Carpenter Technology Corp, Reading 1965 and thecoefficients of expansion of still further alloys can be obtained fromindustrial publications such as the Allegheny Ludlum Blue Sheet Series,Allegheny Ludlum Steel Corporation, Pittsburgh.

Similarly, coefficients of thermal expansion for various other types ofglasses can be obtained from the Kirk-Othmer Encyclopedia of Chemicaltechnology, 2nd Edition, 1965, at page 533 et seq. and particularly page573. See also the Handbook of Glass Manufacture, Ogden PublishingCompany, New York, 1961; or the standard catalogs of glass manufacturerssuch as the Coming Glass Works, Corning, New York; or, Owens- IllinoisGlass, Toledo, or the Schott catalog of the Jena Glass Works.

Reference to the above noted works indicates that the coefficients ofthermal expansion for many magnetic alloys range from about 12 X 10inches per inch per degree C to about 130 X 10 inches per inch perdegree C. Glasses, on the other hand, run from pure quartz (silicondioxide) having a mean thermal coefficient of expansion of about 5.5 X10 inches per inch per degree C through boron trioxide (B having a meancoefficient of thermal expansion of about 150 X inches per inch perdegree C all the way up to sulphur based glasses having coefficients ofthermal expansion a high as 800 X 10 inches per inch per degree C.Hence, a host of various glasses can be combined with standard magneticalloys in the practice of the instant invention. Moreover, variousalloying elements can be added to given standard alloys to adjust theirthermal coefficients of expansion upwardly or downwardly at varioustemperatures or through various temperature ranges; and, variousmodifiers can be added to given glasses in order to adjust their thermalexpansion coefficients. See, for example, Kirk-Othmer at pages 538 and580 et seq.

It should be noted that the above described semiconductor or otherhigh-resistance-layer embodiments can also employ the tape aspectsimilar to that described above in connection with FIG. 8. For example,the highly resistive layers can be formed by mixing hafnium ormolybdenum powder with selenium powder and a volatile binder to form atape such as that described in more detail in U.S. Pat. No. 3,293,072.When heated in the manner described above, therefore, the organic bindervolatizes; and the selenium reacts with the metal to form the desiredhighly resistive layer. Alternatively, a similar tape can be comprisedof aluminum powder mixed with antimony or arsenic powder so that theresulting resistive layer is a semiconductor.

In the example just described the resistivity of the molybdenum-seleniumcompound is about 4000 ohmcm; and that of the hafnium-selenium compoundis about 40,000 ohm-cm.

Various other elements can also be placed in tape form, laminated, andreacted to form the highly resistive inorganic layer. Two metals can bereacted to form an intermetallic compound or semiconductor; a metal suchas molybdenum or hafnium can be reacted with a nonmetal such as sulphurto form a highly resistive inorganic layer; the tape can be comprised ofa powdered semiconductor such as selenium; or set forth in more detailabove the tape can be comprised of an insulator such as glass.

In accordance with still another aspect of the invention the hardness ofthe various insulating layers can be still further improved by heatingthe laminate in various gas-rich atmospheres so that the glass diffuseinto the insulating layers, or the gases can be incorporated into theinsulatinglayers by other methods.

In a preferred embodiment of this aspect of the invention, the entiremethod is carried out in one of the manners described above forfabricating a laminate. The laminate .is first assembled, blanked,annealed, ground, and polished. It is then heated in a hydrogenrichatmosphere so that the hydrogen diffuses into the insulating layers toform metal hydrides which are harder than the pre-hydrogen-diffusedinsulating layers. At the same time the annealing imparts the optimummagnetic properties to the soft magnetic material. Many examples ofsuitable such metal hydrides can be found in Metal Hydrides by Muller,Blackledge and Libowitz, Academic Press, New York, 1968.

Other gases can also be diffused into the metals or otherwise combinedtherewith to obtain beneficial results. Oxygen and nitrogen, forexample, can also be diffused or otherwise combined with the insulatinglayers, but they are more difficult to diffuse than hydrogen.

From the above description it will be apparent that the inventionprovides a structure wherein a magnetic laminate not only has increasedwear characteristics, but is more reliable and more uniformlystructured. Perhaps most importantly, however, the invention provides asoft magnetic laminate that can be annealed after fabrication in orderto obtain the most desirable magnetic properties for the soft magneticmetal.

Although the intermetallic compound embodiment has special advantages,the other embodiments do not require extrusion; nor does the glassembodiment require vapor deposition or the like. Hence, it should beapparent that the glass embodiment is well adapted for the smallmanufacturer to whom extrusion and deposition equipment are not alwaysreadily available.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A laminated magnetically soft material comprising:

a plurality of layers of substantially stress-free magnetically softmetal;

a least one continuous layer of an inorganic electrically insulativematerial having a resistivity of more than about 10 ohm-cm locatedbetween adjacent layers of said substantially stress-free magneticallysoft metal and heat-bonded thereto.

2. The laminate of claim 1 wherein the coefficients of thermal expansionof said magnetically soft metal and said inorganic electricallyinsulative material are substantially the same.

3. The laminate of claim 1 wherein the difference between thecoefficient of thermal expansion of said magnetically soft metal and thecoefficient of thermal expansion of said inorganic electricallyinsulative material is less than about 500 parts per million.

4. The laminate of claim 1 wherein said magnetically soft metal issubstantially fully annealed.

5. The laminate of claim 1 wherein said inorganic electricallyinsulative material includes a solid compound at least one of theconstituents of which is a gas.

6. The laminate of claim 5 wherein said gas is hydrogen and the solidcompound is a hydride.

7. The laminate of claim 1 wherein said magnetically soft metal consistsessentially of 79% nickel, 16% iron, and 4% molybdenum.

8. The laminate of claim 1 wherein the inorganic resistive materialconsists essentially of silicon monoxide.

9. A laminated magnetically soft material comprismg:

a plurality of layers of magnetically soft metal; and

at least one layer of a semiconductor material located between adjacentlayers of said magnetically soft metal and heat-bonded thereto.

10. The laminate of claim 9 wherein said semiconductor material iscomprised of a Group V element reacted with a Group III element.

11. The laminate of claim 9 wherein said semiconductor material isaluminum arsenide.

12. The laminate of claim 9 wherein said semiconductor material isaluminum antimonide.

13. The laminate of claim 9 wherein said semiconductor material consistsessentially of a single semiconductor element.

14. The laminate of claim 13 wherein said element is selenium.

15. The laminate of claim 9 wherein said magnetically soft metal issubstantially fully annealed.

16. The laminate of claim 9 wherein said layer of semiconductor materialincludes a solid compound at least one of the constituents of which is agas.

17. The laminate of claim 16 wherein said gas is hydrogen and said solidcompound is a hydride.

18. A laminated magnetically soft material comprisa plurality of layersof magnetically soft metal; and

at least one layer of a glass located between adjacent layers of saidmagnetically soft metal and heatbonded thereto.

19. The laminate of claim 18 wherein the coefficients of thermalexpansion of said magnetically soft and said glass are substantially thesame.

20. The laminate of claim 18 wherein the difference between thecoefficient of thermal expansion of said magnetically soft metal and thecoefficient of thermal expansion of said glass is less than about 500parts per million.

21. The laminate of claim 18 wherein said magnetically soft metal issubstantially fully annealed.

22. The laminate of claim 18 wherein said glass includes a modifier tomake its coefficient of thermal expansion substantially the same as thecoefficient of thermal expansion of said magnetically soft metal.

23. The laminate of claim 18 wherein said glass includes a modifier sothat the difference between the coefficient of thermal expansion of saidmagnetically soft metal and the coefficient of thermal expansion of saidglass is less than about 500 parts per million.

24. The laminate of claim 18 wherein the mean coefficient of thermalexpansion of said magnetically soft metal is between about 12 X 10inches per inch per degree C and X 10 inches per inch per degree C; and

the mean coefficient of thermal expansion of said glass is between about5.5 X 10 inches per inch per degree C and ISO X 10 inches per inch perdegree C.

25. The laminate of claim 1 wherein said inorganic electricallyinsulative material is a semiconductor.

26. The laminate of claim 25 wherein the coefficients of thermalexpansion of said magnetically soft metal and said semiconductormaterial are substantially the same.

27. The laminate of claim 26 wherein the difference between thecoefficient of thermal expansion of said soft magnetic metal and thecoefficient of thermal expansion of said inorganic electricallyinsulative material is less than about 500 parts per million.

28. The laminate of claim 1 wherein said electrically insulativematerial is a glass.

29. The laminate of claim 28 wherein the coefficients of thermalexpansion of said magnetically soft metal and said glass aresubstantially the same.

30. The laminate of claim 29 wherein the difference between thecoefficient of thermal expansion of said soft magnetic metal and thecoefficient of thermal expansion of said glass is less than about 500per million.

UNITED STATES PATENT OFFICE @ERTHHQAiEIQF CQRRECTHNE 2 gag 5G2 ioril 9lq fi Patent NO J 9 n y D t d 4," J 9 r i It is certified that errorappears in the aboveidentified patent and that said Letters Patent arehereby corrected as shown below:

On fine Cover Sheet, in item {F5 the inventor's name should read ClaytonN Whetstone m gigmd and geaied this f f h Day of Ailgust1975 [SEAL] Anest:

RUTH C. MEX-SON C. MARSHALL DANN Am'srmg ()jjicer ('mmnissimu'r ofParents and Trudcmurkx

1. A LAMINATED MAGNETICALLY SOFT MATERIAL COMPRISING: A PLURALITY OF LAYERS OF SUBSTANTIALLY STRESS-FREE MAGNETICALLY SOFT METAL; A LEAST ONE CONTINOUS LAYER OF AN INORGANIC ELECTRICALLY INSULATIVE MATERIAL HAVING A RESISTIVITY OF MORE THAN ABOUT 10**4 OHM-CM LOCATED BETWEEN ADJACENT LAYERS OF SAID
 2. The laminate of claim 1 wherein the coefficients of thermal expansion of said magnetically soft metal and said inorganic electrically insulative material are substantially the same.
 3. The laminate of claim 1 wherein the difference between the coefficient of thermal expansion of said magnetically soft metal and the coefficient of thermal expansion of said inorganic electrically insulative material is less than about 500 parts per million.
 4. The laminate of claim 1 wherein said magnetically soft metal is substantially fully annealed.
 5. The laminate of claim 1 wherein said inorganic electrically insulative material includes a solid compound at least one of the constituents of which is a gas.
 6. The laminate of claim 5 wherein said gas is hydrogen and the solid compound is a hydride.
 7. The laminate of claim 1 wherein said magnetically soft metal consists essentially of 79% nickel, 16% iron, and 4% molybdenum.
 8. The laminate of claim 1 wherein the inorganic resistive material consists essentially of silicon monoxide.
 9. A laminated magnetically soft material comprising: a plurality of layers of magnetically soft metal; and at least one layer of a semiconductor material located between adjacent layers of said magnetically soft metal and heat-bonded thereto.
 10. The laminate of claim 9 wherein said semiconductor material is comprised of a Group V element reacted with a Group III element.
 11. The laminate of claim 9 wherein said semiconductor material is aluminum arsenide.
 12. The laminate of claim 9 wherein said semiconductor material is aluminum antimonide.
 13. The laminate of claim 9 wherein said semiconductor material consists essentially of a single semiconductor element.
 14. The laminate of claim 13 wherein said element is selenium.
 15. The laminate of claim 9 wherein said magnetically soft metal is substantially fully annealed.
 16. The laminate of claim 9 wherein said layer of semiconductor material includes a soliD compound at least one of the constituents of which is a gas.
 17. The laminate of claim 16 wherein said gas is hydrogen and said solid compound is a hydride.
 18. A laminated magnetically soft material comprising: a plurality of layers of magnetically soft metal; and at least one layer of a glass located between adjacent layers of said magnetically soft metal and heat-bonded thereto.
 19. The laminate of claim 18 wherein the coefficients of thermal expansion of said magnetically soft and said glass are substantially the same.
 20. The laminate of claim 18 wherein the difference between the coefficient of thermal expansion of said magnetically soft metal and the coefficient of thermal expansion of said glass is less than about 500 parts per million.
 21. The laminate of claim 18 wherein said magnetically soft metal is substantially fully annealed.
 22. The laminate of claim 18 wherein said glass includes a modifier to make its coefficient of thermal expansion substantially the same as the coefficient of thermal expansion of said magnetically soft metal.
 23. The laminate of claim 18 wherein said glass includes a modifier so that the difference between the coefficient of thermal expansion of said magnetically soft metal and the coefficient of thermal expansion of said glass is less than about 500 parts per million.
 24. The laminate of claim 18 wherein the mean coefficient of thermal expansion of said magnetically soft metal is between about 12 X 10 7 inches per inch per degree C and 150 X 10 7 inches per inch per degree C; and the mean coefficient of thermal expansion of said glass is between about 5.5 X 10 7 inches per inch per degree C and 150 X 10 7 inches per inch per degree C.
 25. The laminate of claim 1 wherein said inorganic electrically insulative material is a semiconductor.
 26. The laminate of claim 25 wherein the coefficients of thermal expansion of said magnetically soft metal and said semiconductor material are substantially the same.
 27. The laminate of claim 26 wherein the difference between the coefficient of thermal expansion of said soft magnetic metal and the coefficient of thermal expansion of said inorganic electrically insulative material is less than about 500 parts per million.
 28. The laminate of claim 1 wherein said electrically insulative material is a glass.
 29. The laminate of claim 28 wherein the coefficients of thermal expansion of said magnetically soft metal and said glass are substantially the same.
 30. The laminate of claim 29 wherein the difference between the coefficient of thermal expansion of said soft magnetic metal and the coefficient of thermal expansion of said glass is less than about 500 per million. 